Talks between Iran and six world powers entered their last scheduled day on Friday with no sign of a breakthrough over Tehran’s nuclear ambitions.

Baroness Ashton, the European Union’s high representative for foreign policy, held another 90-minute meeting in Geneva with Mohammad Javad Zarif, the Iranian foreign minister.

An EU spokesman described this session as “useful”, but disagreements over crucial issues remain unresolved. In particular, Iran insists that its “right” to enrich uranium must be recognised in any agreement, despite the fact that six United Nations Resolutions ban the country from continuing this process.

America and its allies, meanwhile, want Iran to stop all work on the plutonium reactor at Arak, which could provide another route to the ability to build a nuclear weapon.

A diplomat close to the talks acknowledged that the negotiations were a “long and difficult process” but cautioned that it would be “wrong to read too much into the fact that it’s going slowly”.

After her meeting with Mr Zarif, Lady Ashton briefed senior diplomats from the “P5 plus 1” contact group, consisting of the five permanent members of the Security Council – America, Britain, France, Russia and China – along with Germany.

The talks are scheduled to end later on Friday. Unless an agreement emerges, Lady Ashton, who chairs the “P5 plus 1” will have three options.

She could declare failure and attempt to convene another meeting in a few weeks time. Alternatively, she could simply extend this gathering and continue the talks over the weekend.

Finally, Lady Ashton might ask John Kerry, the US secretary of state, and the other foreign ministers from the “P5 plus 1” powers to come to Geneva to break the deadlock.

Of these possibilities, the second – extending the meeting over the weekend – is seen as most likely at present.

The negotiators are working on a draft text of an agreement, left over from the previous meeting 12 days ago which came close to success.

However, Abbas Araqchi, the Iranian deputy foreign minister, placed the onus on America and the“P5 plus 1” to compromise, accusing them of making “excessive demands”. He told an Iranian news agency: “If the other side show flexibility, we can reach an agreement.”